Pete Parsons sees seasonal flip to rare El Niño

Presenter: The three-month seasonal climate forecast came out Aug. 20. Here’s Pete Parsons:

Pete Parsons: Hey, I’m meteorologist Pete Parsons with the Oregon Department of Forestry. Hope you’re enjoying your summer. I have certainly enjoyed the fact that we’ve had a lot of nice sunny days that have been warm, but not too hot. 

And actually, this analog method predicted that quite well, that we’d have a lot of warm weather, but not a whole lot of the 100+ degree heat.

What we have had is a lot of fires, unfortunately, and a lot of smoke, and we’re still dealing with that. Hopefully we’ll get some relief from that sooner rather than later as we move into the fall season. We’ll see if the seasonal climate forecast helps us out with that. 

We’ll start off again with the ocean temperatures across the tropical Pacific. It’s warming up. Over the past couple of months, we’ve transitioned from what we call ENSO-neutral—it’s neither a La Niña cold ocean nor an El Niño warm ocean, as you’ve probably heard those terms before. If not, you have now.

We’re moving into an El Niño, and it’s going to be probably a very strong one, about as strong as they get. And it’s already up into the moderate category. 

And that affects the jet stream pattern. The jet stream pattern is generated from the ground up. Interestingly enough, we heat the surface and then the surface heats the atmosphere from the bottom up. And it’s the temperature differences around the globe that change the jet stream patterns.

Well, this is a big temperature difference down here from year to year. If it’s cold down here across the tropics, that’s a huge difference in the amount of heat energy going up there rather than being warm. That affects the jet stream patterns worldwide. We know that. And different patterns predict or influence the jet stream in different ways.

It’s not a perfect science, but one of the bonuses for us is there’s a lag time. These temperatures change first, then the jet streams change. And so there’s some inertia with it. So once you get those oceans warming up and they stay warm, depending on the time of year, we default to certain patterns, and I can use that to predict out two or three months.

So it’s middle to late August, we’re going to forecast for September, October and November. We have a developing El Niño down here. Climate Prediction Center thinks again it’s going to be really strong, maybe one of the strongest on record. 

That kind of hurts me when it comes to using analogs, because if it does something that we haven’t seen in the historical record, which we’ve got good records back to about 1950 for here, that’s only about 75 years worth, not very many.

So if we don’t have a year that does what this one does, well, that doesn’t help in terms of finding a good analog. But we’ve got some that are pretty close and that should give us some signal on what’s going on in the atmosphere. 

Now I use some indices to find years in the past that line up with this year. One of them is called the Southern Oscillation Index (SOI). The Southern Oscillation Index is a proxy for the trade wind strength across the tropics. 

Trade winds generally blow from east to west. If the trade winds are strong, then that tends to go with the La Niña, keeps the warmer waters away from the Americas and out into the western Pacific. And if the trade winds weaken, then it allows for warmer waters like we have right now.

So a positive SOI is stronger trade winds. That’s in the La Niña area. That’s what we’ve had for the past couple of winters. We’ve had La Niña conditions.

Then this past spring we came down through ENSO neutral. As the trade winds relax, and that is corresponding with the very strong El Niño. And that’s exactly what the Climate Prediction Center is expecting for this winter.

There’s also another thing that I’m looking at. (I know—there’s a lot going on.) It’s the Pacific Decadal Oscillation. That’s the North Pacific. I don’t know how important this one is, but I know it is. I know it’s important and I don’t want to ignore it.

Right now we’ve got kind of a rare bird because we’re having an El Niño event—El Niños tend to be or have been in the past, mostly associated with the warm phase of the Pacific Decadal Oscillation. 

We don’t have that right now. We haven’t had it for a couple of years. We’ve been in the cold phase of the Pacific Decadal Oscillation, where the warmest waters are out to the west and the cooler, relatively cooler waters are off of our coast.

That doesn’t happen as often with El Niño. It tends to be associated with more La Niñas, which we’ve had recently. We’ve had more La Niñas recently, but we don’t have one now. We’ve got an El Niño and a strong one at that lined up with the cool phase of the Pacific Decadal Oscillation. That’s kind of rare.

I couldn’t find three good cold years that line up. That’s how rare they are. Could only find two all the way back. So here’s what we’re expecting in September: That split begins to develop and it pretty consistently is handled by all three of these analogs for at least one month. 

They all put anomalous troughing, more troughing than normal aloft, more jet stream energy than normal coming into the West Coast in September. And I’m looking at the numbers here. All three of these top analog years give us a cooler and wetter than normal September, at least for sections of Oregon. Not necessarily every section.

I took them put them down for Western Oregon, cooler and wetter than normal. That’s significant. What they’re saying is that we’re going to see a switch get flipped, and we’re going to go from this warm, dry condition more than likely boom into a cool, wet regime with storms coming in a little stronger than normal off the Pacific in September. 

They’re saying colder than normal for September. Not at the beginning of the month though. At the beginning of the month, all three of these analog years had 90+ degree heat in northwest Oregon, Western Oregon. They kept the heat through the first week to 10 days of the month, so it starts out warm. 

‘Oh, that guy is always talking about. It’s hot. I’m burning up,’ you know. Hang on. Around the middle of the month, they went and they flipped over and the storms came in and bang! Did it cool off. 

So the second half of the month is way cooler than normal. So it made the whole month a little cooler than normal because it’s going to start out warm according to those things and the precipitation above normal, he said.

Wow. That’s great. Well, it is great to start to help to put out the fires if it happens. But keep in mind we don’t get normally a lot of precipitation still in September. That’s not the wettest month on earth for us. You got to get into October and November and December. November is really wet. You got to make that transition.

So even though these this is an percent of average—so 150%, 160% of average. They all are going to get just that’s a fair chunk of rain, but it’s not a whole lot of rain because it’s typically a dry month. 

So don’t get too excited about it. But it would help. It would help a lot to get some wet weather coming in early.

So I expect that to start off warm and dry and then boom, cool and wet. ‘Hello Fall,’ a week or so early. We’ll see. That’s what the analogs say. And they say it pretty consistently. That’s probably my highest conviction forecast for this three month period because that’s really about the only time they all say the same thing is in September-October.

They start to diverge. But they do keep one thing in common. These are the same three analog years. Again, they still have that split flow. That’s what El Niño tends to produce here. 

November: Same idea. The same basic flow pattern is still there. It’s a split flow jet stream that’s strengthening because we’re getting into the later fall.

And we’re going to see a lot of storminess into California. That looks like a slam dunk. A lot of rain, a lot of snow in the Sierra. And that can sometimes creep up into Southern Oregon. But that’s getting more into the winter forecast.

But that’s what we’re looking at. And Southern Oregon’s got a better chance of above normal snowpacks than northern Oregon this winter because of that.

But the reality is for temperatures. because of the mix of the two, we see right near average, maybe even still a little bit on the cool side, October, November. And that’s what El Niños tend to do. If you want to think about the winter El Niño early, you tend to get things boom. It comes in earlier, the winter, the fall, winter, the cool-off.

And that’s what we’re going to look at, I think, for this winter. But then it turns mild. La Niña, you can have nice weather hanging on late, man. You can get nice weather into September / October. It’s sunny, it’s beautiful. 

But when winter comes in later, it gets really cold. January, February, it has the opposite effect on us. That’s here in the Pacific Northwest, especially in Oregon. 

Precipitation by November for the three-month period: The main picture, developing El Niño. That’s likely. It’s already here. It’s likely to be strong. Predictions are it’ll be very strong. Maybe the strongest. Who knows?

That’s likely to give us the split flow jet stream pattern as we head into the fall and more troughiness along the West Coast. A lot more energy coming in from the jet stream than normal, especially in the California maybe. Or maybe not making it as far north as Oregon.

That’ll bring in some cooler storms, boom! Right there, probably in the middle of September. And then they’ll get kind of split and not as much strength to them maybe as we get into November. But we’ll start to see some potent storms heading into California, that kind of idea.

How’s that going to play out as we go into the winter? I know you’re thinking about that. I’m thinking about that. 

Generally speaking, El Niños don’t tend to produce a lot of cold and snow in the lowlands west side as you get into winter, but cold phase PDO with the El Niño can. And have.

1972, which is one of our top analogs right now, did in December, really nailed us with a big cold outbreak in December for all of Oregon. It was one of the coldest of the century and long-lasting and all that, and not a lot of snow with it, but it was cold.

So it can happen. So we’ll see. We’ll see on that. But the overall tends to be not as good a snowpack for the northern Cascades as for the southern Cascades. 

And it tends to be a big snowpack for the Sierra. So for the Southwest this could really help the drought situation in the Southwestern U.S. Wow, could really really do something for them. 

Here’s the three-month: a little bit on the cool side and precipitation near average. You get the wetter part early, and then by November it’s going back to a little on the dry side. Shows up as a little dry, so nothing real impressive on the precipitation after what looks like. Might be a good start. 

And then it kind of backs off a little bit. That’s the idea. But I think we’re in for some interesting weather, cold phase PDO, the North Pacific and a strong El Niño is rare indeed. And that’s what it looks like we’re going into this winter.

In the meantime, get out and enjoy some of this nice summer weather. It looks like it’s going to continue to be good and kind of get yourself ready for what could be a pretty interesting transition to some cooler, damp weather, maybe around the middle of September. But until then, it looks like it’s going to be pretty darn nice.

So we’ll catch up with you and take a look at the forecast again and see if it needs some updates next month. Take care.

Presenter: You can view the complete PDF with the three-month seasonal forecast online. Search for ‘Seasonal Climate Forecast’ at oregon.gov.